CHAPTER 26

Optic Disc Abnormalities

Developmental Anomalies

Optic Nerve Hypoplasia

Optic nerve hypoplasia (ONH) is the most common optic disc anomaly encountered by ophthalmologists. Histologically, optic nerve hypoplasia is characterized by a decreased number of optic nerve axons. Clinically, the disc is pale or gray and smaller than normal. This condition can be unilateral or bilateral and is often asymmetric (Fig 26-1). It may be associated with a yellow to white ring around the disc (double-ring sign). The edge of the outer ring corresponds with the normal junction between the sclera and the lamina cribrosa; the outer ring itself corresponds with the abnormal extension of the retina and pigment epithelium over the outer portion of the lamina cribrosa; and the inner ring corresponds to the hypoplastic optic nerve. Because the size of the outer ring often corresponds to the normal disc diameter, careful observation is necessary to avoid interpreting the hypoplastic disc/ring complex as a normal-sized optic nerve with normal cup–disc ratio. The vascular pattern is also abnormal and can be associated with too few or too many disc vessels. Retinal vascular tortuosity is common.

Figure 26-1 Optic nerve hypoplasia. A, Normal right optic nerve. B, Hypoplastic left optic nerve.

Visual acuity ranges from normal to no light perception and is related to the integrity of the macular fibers; it often does not correlate with the overall size of the disc. Localized visual field defects and visual field constriction are common. Children with bilateral ONH often present with congenital sensory nystagmus, and those affected unilaterally often present with sensory strabismus. Because patients with ONH can have strabismus, unilateral vision loss may partially result from

Figure 26-3 Coronal T2-weighted MR image through the orbits: the right optic nerve is smaller and more T2 hyperintense

than the left optic nerve. (Courtesy of Jane L. Weissman, MD.)

Patients with ONH may also have cerebral hemisphere or pituitary gland abnormalities. Cerebral hemisphere abnormalities include schizencephaly, periventricular leukomalacia, and encephalomalacia. They occur in approximately 45% of patients with ONH and are associated with neurodevelopmental defects.

Approximately 15% of patients with ONH have pituitary gland abnormalities. MRI in these patients reveals an ectopic posterior pituitary bright spot at the upper infundibulum. This finding is associated

with pituitary hormone abnormalities, including growth hormone deficiency, hypothyroidism, hyperprolactinemia, panhypopituitarism, and diabetes insipidus. A history of neonatal jaundice suggests hypothyroidism; neonatal hypoglycemia or seizures indicate possible panhypopituitarism. Patients with ONH and diabetes insipidus can have problems with thermal regulation and must be monitored carefully during febrile illnesses. Referral to a pediatric endocrinologist is indicated for patients with either clinical signs of endocrinologic dysfunction or pituitary abnormalities on MRI.

ONH denotes injury to the optic nerve prior to complete development and can occur from any prenatal or perinatal injury. Frequently, the etiology is unknown. ONH has been associated with maternal ingestion of phenytoin, quinine, and LSD, as well as with fetal alcohol syndrome. Segmental hypoplasia may occur in children whose mothers have type 1 diabetes mellitus.

Children with periventricular leukomalacia (PVL) display an unusual form of ONH. The optic nerves demonstrate a large cup within a normal-sized optic disc. This form of ONH occurs secondary to transsynaptic degeneration of optic axons, which is caused by bilateral lesions in the optic radiations.

Brodsky MC, Glasier CM. Optic nerve hypoplasia. Clinical significance of associated central nervous system abnormalities on magnetic resonance imaging. Arch Ophthalmol. 1993; 111(1):66–74.

Garcia-Filion P, Borchert M. Optic nerve hypoplasia syndrome: a review of the epidemiology and clinical associations. Curr Treat Options Neurol. 2013;15(1):78–89.

Morning Glory Disc Anomaly

Morning glory disc anomaly is caused by either an abnormal closure of the embryonic fissure or abnormal development of the distal optic stalk at its junction with the primitive optic vesicle. The anomaly is a funnel-shaped excavation of the posterior fundus that incorporates the optic disc. The surrounding retinal pigment epithelium is elevated, with an increased number of blood vessels looping at the edges of the disc (Fig 26-4). A central core of white glial tissue occupies the normal position of the cup. This tissue may have contractile elements, and the optic cup can sometimes be seen to open and close with some periodicity. Morning glory disc anomaly occurs more frequently in females and is typically unilateral. Visual acuity ranges from 20/20 to no light perception, but it is usually 20/100–20/200. Serous retinal detachments occur in approximately one-third of affected patients. Morning glory disc anomaly has been associated with basal encephalocele in patients with midfacial anomalies, PHACE syndrome (posterior fossa malformations, hemangiomas, arterial lesions, cardiac and eye anomalies), and abnormalities of the carotid circulation (moyamoya disease). Therefore, MRI and MR angiography of the brain should be obtained in patients with morning glory disc anomaly.